It is well-know that the rotary coupling for transferring fluids is a special component which, when used, e.g., in an off-shore facility, makes it possible for pressurized fluid to flow from a non-rotary structure comprising the system of single-point mooring such as, a single mooring, to a vessel moored to the same structure. The moored vessel is free to rotate around the single mooring on the horizontal plane, in order to arrange itself in a position of minimum resistance to waves, streams and wind.
Several types of rotary couplings for transferring fluids are already known in the prior art.
At first, single-way rotary couplings were developed. Later, the adoption of the single moorings for tankers, as floating systems for hydrocarbon production, caused the need for having available multi-passage rotary couplings. On the other hand, the need to operate with fluids displaying different compositional characteristics, and the different conditions of temperature and pressure they are at, led the designers to develop multi-passage rotary couplings with modular structure, i.e., rotary couplings comprising a plurality of modules assembled along a common vertical axis. In such a way, each module can be designed independently from the other modules, based upon the function of pressure and temperature, or based on the composition of the fluid which is expected to flow through the module.
The prior art modular, multi-passage, rotary couplings are comprised of a plurality of mutually superimposed modular elements, i.e., couplings, wherein each of said modules is suitable for transferring a fluid, substantially comprise, for each module, an inner fixed ring and an outer rotary ring connected with each other and kept mutually concentric by at least one bearing. Said inner fixed ring and said outer rotary ring have bound between each other a toroidal chamber sealed by circular dynamic seals. This chamber puts the ducts for fluid passage provided in said rings into communication with one another, thus enabling the fluid to flow through the module also when said rings are rotated relative to each other. A pipe is then connected with each fixed ring of the modular multi-passage coupling, generally fastened to it by means of flanges, screw-threadings, and so on. This pipe also runs through the fixed rings of the underlying modules. Each fixed ring being further provided with an inner free region, so as to allow all of the fixed pipes--and namely, its own pipe, and the pipes relevant to the overhanging modules--to run through the same module.
To date, all of the modules of a multi-passage, rotary coupling are generally at the same diameter. But, clearly inasmuch as the various fixed pipes are each connected with the fixed ring of the relevant module--with the number of the pipes which run through the subsequent modules obviously decreasing--, said subsequent modules can be given a progressively decreasing diameter with consequent advantageous effects on the dynamic seals. The performance of the dynamic seals, as known, increased with decreasing diameters, besides increasing, of course, with decreasing values of pressure and temperature of the fluid they are designed to contain.
Actually, in particular for fluids which are under high temperature and high pressure conditions, it is preferable to design the modular multi-passage rotary coupling with a tapered configuration, i.e., with modules of progressively decreasing diameter. In such couplings, the fixed pipes which run through the interior of each fixed ring must be given a proper bend in order to be able to match the reduced inner free region of the fixed rings of the successive modules of the coupling.
Unfortunately, such known embodiments have some drawbacks. The most serious of these drawbacks derives from the types of disengageable connection adopted heretofore in order to fasten the fixed pipes to the fixed rings and is given by the large overall dimensions in the radial direction of the modules of the coupling, as determined by the need for providing a large surface area for the free region inside the interior of the fixed rings, or due to the possible presence of a flange of the pipe to be connected with the fixed ring, or in order to be able to possibly screw down a bent fixed pipe onto the fixed ring.
Such a drawback requires using large-diameter dynamic seals, with a consequent considerable reduction in the reliability and reduction in the useful life of the same coupling.
Another drawback shown by the prior art rotary couplings which is caused by the large radial overall dimensions is given by the fact that dynamic mechanical seals show a considerably higher wear resistance than the dynamic seals which are made of polytetrafluoroethylene or other plastic materials, as presently used in the rotary couplings used for transferring fluids in general, in particular, if the fluid contains abrasive substances. Mechanical seals, therefore, endow the same coupling with characteristics of long useful life, requiring an extremely reduced servicing.
Further drawbacks shown by prior art modular multi-passage rotary couplings are then due to 1) the difficult access for interventions from the upper side of the coupling, for example for maintenance reasons, in that the lines are not easily accessed from the top side; 2) to the difficulty of applying easily replaceable devices in order to compensate for the erosion effect of the abrasive particles suspended in the fluid, as well as to difficult replacement of a modular element under failure conditions of the coupling with another space modular element, in order to be able to continue to use the rotary coupling; and 3) with the repair operations, which require the shutdown of the facility, having to be delayed until the most favorable time.
The object of the present invention is of obviating the above said drawbacks and, therefore, of providing a modular multi-passage rotary coupling for transferring fluids, which has greatly reduced overall dimensions in the radial direction, with the consequent possibility of the use of dynamic seals of mechanical type. Another object is to make it easy to access the lines from the top side and to make it easy to apply replaceable devices in order to protect the coupling against the failures caused by abrasion. A still further object is to make possible an immediate by-pass connection to be produced from a module under failure conditions to a spare module.